Answer on Mechanics | Kinematics | Dynamics Question for uzair zaidi

An indestructible bullet 2.00 cm long is fired straightthrough a board that is 10.0 cm thick. The bullet strikesthe board with a speed of 420 m/s and emerges with aspeed of 280 m/s. (a) What is the average accelerationof the bullet as it passes through the board? (b) What isthe total time that the bullet is in contact with theboard? (c) What thickness of board (calculated to0.1 cm) would it take to stop the bullet, assumingthe bullet’s acceleration through all parts of the boardis the same?

Expert's answer

Total length in collision is 14smS=at^2/2+v0tv1=v0-ata=(v0-v1)/tS=-(v0-v1)t/2+v0t=(v0+v1)t/20.14=350ta=140/tt=0.0004a=3500 m/sSo, for full stop:at=v0t=v0/aS=at^2/2+v0tS=v0^2/2a+v0^2/aS=3v0^2/2aS=75.6 sm